Hepatitis B virus (HBV) is a double stranded DNA virus that may be carried by as much as 20% or more of the apparently healthy population in certain parts of the world, such as Africa, Asia and the Pacific Region. Principles and Practice of Clinical Virology, 3rd Edition, Chapter 2: Hepatitis Viruses, pp. 162-180. The reservoir of carriers worldwide is estimated at a number over 300 million. HBV was originally thought to be spread exclusively by blood and blood products, although it now appears that HBV can also be transmitted by intimate contact, such as sexual contact, and other routes may also be possible. Thus, transmission of infection may result from accidental inoculation of minute amounts of blood, or fluid contaminated with blood, during medical, surgical and dental procedures; immunization with inadequately sterilized syringes and needles; intravenous or percutaneous drug abuse; tatooing; car, nose and other piercing; acupuncture; laboratory accidents; and, accidental inoculation with razors and similar objects that have been contaminated with blood. Id.
HBV comprises at least three morphologically distinct forms, an about 22 nm spherical particle, a tubular form of roughly the same diameter that is composed of the virus surface protein, and a 42 nm double-shelled virion. The core or nucleocapsid of HBV comprises the genome surrounded by a second protein, hepatitis B core antigen (HBcAg; also known as p22). Other HBV antigens include the HBsAg and HBeAg. Id.; Zuckerman, A. J., Human Viral Hepatitis (North-Holland/American Elsevier, Amsterdam, 1975).
The genomes of a variety of isolates of HBV have been cloned and the complete nucleotide sequence thereof determined. Although there is some variation in sequence (up to about 12% of nucleotides) between these isolates, the genetic organization and other essential features are conserved. The genome is around 3200 base pairs in length and analysis of the protein coding potential reveals four conserved ORFs. The four ORFs are located on the same DNA strand and the strands of the genome have accordingly been designated the plus (incomplete strand) and minus (complete strand) as shown in FIG. 1 hereto.
The core protein (HBcAg) is the major component of the nucleocapsid and includes an arginine-rich domain in the carboxyl terminus that presumably interacts with the viral nucleic acid. Antibodies against this protein (anti-HBcAg) are important in diagnosis because anti-HBcAg tends to maintain a relatively significant presence in the blood over time. Principles and Practice of Clinical Virology, 3rd Edition, Chapter 2: Hepatitis Viruses, p. 170.
Assays for the diagnosis of the potential presence of HBV in a patient, as indicated by the presence of the HBcAg, are known in the art. However, it is believed that such assays do not detect very small quantities of HBcAg in a sample, and therefore assays having increased sensitivity for HBcAg are needed to enhance the detection of HBcAg, and therefore HBV. Such a need is accentuated due to the need to inhibit transmission of HBV via the blood, for example due to blood transfusions and other blood-related activities.
Thus, there has gone unmet a need for products and methods capable of highly specific, highly sensitive detection of HBV. There has also gone unmet a need for products and methods capable of eliciting, or enhancing the elicitation of, an immune response to HBV, especially an immunoprotective immune response to HBV. The present invention utilizes properties of the HBcAg of HBV to provide these advantages, as well as other related advantages.